Some wireless communication networks are completely proprietary, while others are subject to one or more standards to allow various vendors to manufacture equipment for a common system. One standards-based network is the Universal Mobile Telecommunications System (UMTS), which is standardized by the Third Generation Partnership Project (3GPP). 3GPP is a collaborative effort among groups of telecommunications associations to make a globally applicable third generation (3G) mobile phone system specification within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU). The UMTS standard is evolving and is typically referred to as UMTS Long Term Evolution (LTE) or Evolved UMTS Terrestrial Radio Access (E-UTRA).
According to Release 8 of the E-UTRA or LTE standard or specification, downlink communications from a base station (referred to as an “enhanced Node-B” or simply “eNB”) to a wireless communication device (referred to as “user equipment” or “UE”) utilize orthogonal frequency division multiplexing (OFDM). In OFDM, orthogonal subcarriers are modulated with a digital stream, which may include data, control information, or other information, so as to form a set of OFDM symbols. The subcarriers may be contiguous or non-contiguous and the downlink data modulation may be performed using quadrature phase shift-keying (QPSK), 16-ary quadrature amplitude modulation (16QAM), or 64QAM. The OFDM symbols are configured into a downlink sub frame for transmission from the base station. Each OFDM symbol has a temporal duration and is associated with a cyclic prefix (CP). A cyclic prefix is essentially a guard period between successive OFDM symbols in a sub frame. According to the E-UTRA specification, a normal cyclic prefix is about five (5) microseconds and an extended cyclic prefix is about 16.67 microseconds. The data from the serving base station is transmitted on physical downlink shared channel (PDSCH) and the control information is signaled on physical downlink control channel (PDCCH).
In contrast to the downlink, uplink communications from the UE to the eNB utilize single-carrier frequency division multiple access (SC-FDMA) according to the E-UTRA standard. In SC-FDMA, block transmission of QAM data symbols is performed by first discrete Fourier transform (DFT)-spreading (or precoding) followed by subcarrier mapping to a conventional OFDM modulator. The use of DFT precoding allows a moderate cubic metric/peak-to-average power ratio (PAPR) leading to reduced cost, size and power consumption of the UE power amplifier. In accordance with SC-FDMA, each subcarrier used for uplink transmission includes information for all the transmitted modulated signals, with the input data stream being spread over them. The data transmission in the uplink is controlled by the eNB, involving transmission of scheduling grants (and scheduling information) sent via downlink control channels. Scheduling grants for uplink transmissions are provided by the eNB on the downlink and include, among other things, a resource allocation (e.g., a resource block size per one millisecond (ms) interval) and an identification of the modulation to be used for the uplink transmissions. With the addition of higher-order modulation and adaptive modulation and coding (AMC), large spectral efficiency is possible by scheduling users with favorable channel conditions. The UE transmits data on the physical uplink shared channel (PUSCH). The physical control information is transmitted by the UE on the physical uplink control channel (PUCCH).
E-UTRA systems also facilitate the use of multiple input and multiple output (MIMO) antenna systems on the downlink to increase capacity. As is known, MIMO antenna systems are employed at the eNB through use of multiple transmit antennas and at the UE through use of multiple receive antennas. A UE may rely on a pilot or reference signal (RS) sent from the eNB for channel estimation, subsequent data demodulation, and link quality measurement for reporting. The link quality measurements for feedback may include such spatial parameters as rank indicator, or the number of data streams sent on the same resources; precoding matrix index (PMI); and coding parameters, such as a modulation and coding scheme (MCS) or a channel quality indicator (CQI). For example, if a UE determines that the link can support a rank greater than one, it may report multiple CQI values (e.g., two CQI values when rank=2). Further, the link quality measurements may be reported on a periodic or aperiodic basis, as instructed by an eNB, in one of the supported feedback modes. The reports may include wideband or subband frequency selective information of the parameters. The eNB may use the rank information, the CQI, and other parameters, such as uplink quality information, to serve the UE on the uplink and downlink channels.
A home-basestation or femto-cell or pico-eNB or relay node (RN) is referred to as hetero-eNB (HeNB) or a hetero-cell or hetero base station in the sequel. A HeNB can either belong to a closed subscriber group (CSG) or can be an open-access cell. HeNBs are used for coverage in a small area (such as a home or office) in contrast with eNBs (also referred to as macro eNBs or macro-cells) which are typically used for coverage over a large area. A CSG is set of one or more cells that allow access only to a certain group of subscribers. HeNB deployments where at least a part of the deployed bandwidth (BW) is shared with macro-cells are considered to be high-risk scenarios from an interference point-of-view. When UEs connected to a macro-cell roam close to a HeNB, the uplink of the HeNB can be severely interfered with particularly when the HeNB is far away (for example >400 m) from the macro-cell, thereby, degrading the quality of service of UEs connected to the HeNB. The problem is particularly severe if the UE is not allowed to access the HeNB that it roams close to (for example, due to the UE not being a member of the CSG of the HeNB). However, even if the UE roams close to a HeNB that it is allowed to access, the interference can be substantial. Currently, the existing Rel-8 UE measurement framework can be made use of to identify the situation when this interference might occur and the network can handover the UE to an inter-frequency carrier which is not shared between macro-cells and HeNBs to mitigate this problem. However, there might not be any such carriers available in certain networks to handover the UE to. Further, as the penetration of HeNBs increases, being able to efficiently operate HeNBs on the entire available spectrum might be desirable from a cost perspective. Several other scenarios are likely too including the case of a UE connected one HeNB experiencing interference from an adjacent HeNB or a macro cell. The following types of interference scenarios have been identified.
HeNB (aggressor)→MeNB (victim) downlink (DL)
HUE (aggressor)→MeNB (victim)uplink (UL)
MUE (aggressor)→HeNB (victim)UL
MeNB (aggressor)→HeNB (victim)DL
HeNB (aggressor)→HeNB (victim)on DL
HeNB (aggressor)→HeNB (victim)on UL.
In this disclosure, we discuss HeNB uplink (UL) interference and downlink (DL) interference problems in further detail and propose a method that can enable a more effective co-channel/shared channel deployment of HeNBs in LTE Rel-9 systems and beyond.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon a careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.